Algae will consume your nitrates.
What you might want to do is get a refugium going with macro algae in it like spaghetti (chaetomorpha) algae in it, which you can trim to help keep your nitrates down.
Having brown algae (diatoms) could be a result of having silicates in your water. What kind of water do you use? Tap, RO, RO/DI?